I do a combination of the two. I start out with a greyscale drawing, add color to it half way through the process and then work with colors on top later to get away from that colored greyscale drawing look.

Yeah, it works pretty well, and lets you focus on getting your values right earlier in the process. You should experiment with different methods of adding color though. Just using layers set to Color blending mode isn't necessarily the best way to go about it. I personally prefer using Photoshop's Gradient Map adjustment layers, as they give you more control over how light values and dark values are colored.

I think it's pretty important to get to know the different types of layers you can create, and get comfortable with using them. It's a good place to start, and once you do, it opens up some interesting options for how to draw things. Fortunately, the most basic types of layers, like Multiply layers or Overlay layers etc., work just like in any other programs. But Photoshop has got some unique ones too, like the Gradient Map adjustment layer I mentioned.Good luck!